1. Technical Field
This invention is directed towards regenerative heat pump system and method using a working fluid or refrigerant and an adsorbent material.
2. Discussion of the Invention
Heat pumps using solid adsorbent beds are well known as shown by U.S. Pat. Nos. 4,610,148, 4,637,218 4,694,659, 5,025,635, 5,046,319 and 5,079,928. In general since sorbents take up the working fluid when cooled and desorb the working fluid when heated, heat pumps are said to be heat driven. Often in adsorbent and chemisorbent heat pumps two beds of sorbents are used, one to adsorb the working fluid while the other bed is desorbing the working fluid. Alternate heating and cooling of the beds is the conventional procedure. When used in air conditioning, heat from an interior room may be used to evaporate the working fluid in an evaporator with heat rejection to the environment at ambient temperatures.
In all of such systems the efficiency of the apparatus is measured by its coefficient of performance or "COP". By the term "COP" as used herein is meant the ratio of heating or cooling work performed divided by the amount of power required to do the work. Since cooling COP.sub.S, or COP.sub.CS, are generally lower than heating COP.sub.S, or COP.sub.HS, many systems are rated on their cooling COP.sub.S.
U.S. Pat. No. 4,637,218 mentions cooling COP.sub.S between 1 and 2 and heating COP.sub.S between 2 and 3. In U.S. Pat. No. 4,637,218 a hot coolant is pumped from a hot 204.4.degree. C. sorbent compressor to a cooler 37.8.degree. C. sorbent compressor, while at the same time cold coolant is pumped from the cooler sorbent compressor to the hotter sorbent compressor. Both compressors exchange heat yielding a typical heat regeneration efficiency of about 80%. The remainder of the heat is supplied by a boiler at about 204.degree. C.
U.S. Pat. No. 4,610,148 reports a theoretical heating COP of about 3 and a cooling COP of about 2, and, a calculated operating COP.sub.H of about 2.6 and a calculated operating COP.sub.C of about 1.6.
FIG. 3 of U.S. Pat. No. 4,694,659, which is concerned with a dual sorbent bed heat pump, shows heating and cooling COP's as a function of a dimensionless thermal wavelength parameter.
Cryogenic cooler systems for sorption refrigerators using a sorption compressor, a heating/cooling loop and a Joule-Thomson expansion valve, or "J-T" valve, with methane as a refrigerant gas and charcoal as the adsorbent, are disclosed in articles entitled "High Efficiency sorption Refrigerator Design", and, "Design and Component Test Performance of an Efficient 4 W, 130 K Sorption Refrigerator" in Advances In Cryogenic Engineering, Vol. 35, Plenum Press, New York, 1990. Desorption occurs at 4.46 MPa (646 psia), i.e. P.sub.H, and adsorption at 0.15 MPa (22 psia), i.e. P.sub.L, or a pressure ratio of about 30, i.e. P.sub.H /P.sub.L =30. Methane is expanded from 4.46 MPa to 0.15 MPa to achieve cooling below 130.degree. K. (-143.degree. C.). The sorbent is heated from 240.degree. K. (-33.degree. C.) to 600.degree. K. (327.degree. C.) to desorb the methane.
U.S. Pat. Nos. 4,875,346 and 5,157,938 disclose cryogenic refrigeration systems in which heat is transferred by helium heat transfer gas from a higher temperature circuit to a lower temperature circuit. When heat is to be transferred, helium is charged to annular gas-gaps between concentric higher and lower temperature circuits. The helium heat transfer fluid is not recycled in a closed loop bt exhausted to a vacuum such as outer space leaving a vacuum in the gas-gaps when no heat is to be transferred between circuits. The working fluids used in the system are xenon, krypton and oxygen.
U.S. Pat. No. 4,732,008 uses heat from a high condenser and high absorber of a higher temperature solution pair to heat a low generator of a lower temperature solution pair.
U.S. Pat. No. 4,827,728 uses a heat exchanger for heating the generator of the absorption circuit with heat rejected from the condenser and absorber of a medium absorption circuit.
U.S. Pat. Nos. 5,025,635 and 5,079,928 transfer heat with a heat transfer fluid from one chemisorbent to another chemisorbent, e.g. from MgBr.sub.2 to CoBr.sub.2 to CoCl.sub.2 to CaBr to SrBr.sub.2.
U.S. Pat. No. 5,042,259 discloses a regenerative hydride heat pump system for regenerating the sensible heat of the system which involves a series of at least four canisters containing a lower temperature performing hydride and a series of at least four canisters containing a higher temperature performing hydride. Each canister contains a heat conductive passageway through which a heat transfer fluid is circulated so that sensible heat is regenerated.
Gas Research Institute Report No GRI-88/0273 of October 1988, entitled Solid-Vapor Adsorption Refrigeration System Development, discusses solid-vapor inorganic complex compounds such as hydrates and amines and cycles for use in industrial refrigeration applications. Vapor pressure plots of compounds CC260-1260 and CC260-1300, which are solid inorganic complex compounds and are useful adsorbents for use in this invention, are found on pages 23 and 29 of Report No. GRI-88/0273.
U.S. Department of Energy, Paper No. DE91 010442, entitled Development of a High-Efficiency, Gas-Fired, Absorption Heat Pump for Residential and Small-Commercial Applications, September 1990, by Phillips Engineering Co. discusses the generator-absorber heat-exchange (GAX) cycle using ammonia-water as the fluid pair; and FIG. 14 thereof is a schematic flow diagram of the GAX absorption unit.
Chemisorbents useful for the higher temperature circuit of this invention are set forth in U.S. Pat. Nos. 4,848,994, 5,025,635 and 5,079,928.
A two staged adsorption system is disclosed in an article entitled "Improving Adsorption Cryocoolers By Multi-stage Compression And Reducing Void Volume", Cryogenics, 1986, Vol 26, page 456, by S. Bard. Refrigerant is passed between carbon adsorbent stages. However, a circuit for the heat transfer fluid for regenerating heat was not shown. It is understood that the heat was simply exhausted and not regenerated.
U.S. Pat. No. 5,025,635 discloses staged adsorbers each containing different adsorbents, i.e. MgBr.sub.2, CoBr.sub.2, CoCl.sub.2, CaBr.sub.2 and SrBr.sub.2 in a single housing
U.S. Pat. No. 5,079,928 mentions that some reactors in a staged system can be combined into a single reactor.
Regenerative heat transfer fluid circuits for a single stage system are disclosed in U.S. Pat. No. 5,046,319.
Other references of interest are U.S. Pat. Nos. 4,732,008, 4,827,728 and 4,848,994, and an article entitled "Sorption Cooler Technology Development At JPL", Cryogenics, 1990, Vol 30, page 239, by J. A. Jones.